1. Field of the Invention
The present invention relates to a multibeam scanner.
2. Description of Related Art
Beam scanners used in laser beam printers and the like use a polygon mirror or the like to deflect an optical beam that is modulated according to image signals, thereby scanning a photosensitive material in a main scanning direction, while moving the photosensitive material in an auxiliary scanning direction to expose the photosensitive material to form an image thereon.
In recent years, a multibeam scanner has been proposed for performing main scans over a plurality of scanning lines simultaneously using a plurality of laser beams to irradiate the photosensitive material. By scanning a plurality of scanning lines in the main scanning direction simultaneously, this multibeam scanner can expose a photosensitive material in a shorter time than scanners using only one laser beam. Further, since the laser beams that scan the photosensitive material simultaneously are maintained at fixed intervals or distances in relation to one another, irregular intervals between beams is less likely to occur.
Sometimes it is desirable to print an image by altering its recording density in the auxiliary scanning direction. A measure for dealing with this case is described for a beam recorder proposed in Japanese Examined Patent Application Publication No. HEI-4-3147. In this method, the number of lit laser diodes is decreased in order to increase the interval between scanning lines that are scanned simultaneously.
Although it is possible to decrease the recording density for printing using this type of conventional beam recorder, the velocity in the auxiliary scanning direction is the same as when printing at a higher recording density. Accordingly, it is impossible to improve the printing speed even when reducing the resolution.
In view of the above-described drawbacks, it is an objective of the present invention to provide an improved multibeam scanner which is capable of printing faster in the auxiliary scanning direction when printing at a low resolution than when printing at a high resolution and which is still capable of exposing images at a high rate of speed with little loss in image quality.
In order to attain the above and other objects, the present invention provides a multibeam scanning device, comprising: a resolution setting unit setting at least a first resolution; a photosensitive medium moving unit moving a photosensitive medium in a predetermined moving direction, the photosensitive medium moving unit moving the photosensitive medium in the predetermined moving direction at a first velocity that corresponds to the first resolution, an auxiliary scanning direction being defined as a direction opposite to the predetermined moving direction; a light beam unit that emits a plurality of light beams; a light beam modulation unit that modulates the plurality of light beams dependently on image signals; and a beam deflecting unit deflecting the plurality of modulated light beams to simultaneously scan the plurality of light beams on a corresponding plurality of scanning lines that extend along a predetermined main scanning direction on the photosensitive medium, while the photosensitive medium moves in the predetermined moving direction, thereby exposing a corresponding image on the photosensitive medium, the main scanning direction being substantially orthogonal to the moving direction, the plurality of scanning lines being arranged adjacent to one another and being separated from one another by a first interval in the auxiliary scanning direction, the beam deflecting unit deflecting the plurality of light beams in the main scanning direction repeatedly to form a successive sets of plural scanning lines while the photosensitive medium moving unit moves the photosensitive medium in the predetermined moving direction, thereby forming the successive sets of scanning lines to be arranged and to be separated from one another by a second interval in the auxiliary scanning direction, the second interval having a value corresponding to the first velocity and greater than a value of the first interval, the plurality of light beams including a first light beam that forms, in each set, a first scanning line that is located adjacent to a scanning line in a preceding set of scanning lines, and a second light beam that forms, in each set, a second scanning line that is located adjacent to a scanning line in a subsequent set of scanning lines, the light beam modulation unit modulating, for the first resolution, the second light beam, that forms the second canning line of each set, and the first light beam, that forms the first scanning line of another set next to the each set, based on the same image signal.
The value of the second interval may preferably be in a range greater than the value of the first interval and smaller than a value second times as large as the value of the first interval.
The beam deflecting unit may deflect the plurality of modulated light beams to simultaneously scan the plurality of light beams at a predetermined main scan velocity along the predetermined main scanning direction on the photosensitive medium. The resolution setting unit may be capable of changing a resolution from the first resolution to another resolution. The photosensitive medium moving unit may change, in response to change of the resolution, the moving velocity of the photosensitive medium in the predetermined moving direction from the first velocity into another velocity, thereby changing the value of the second interval according to the set resolution.
The resolution setting unit may be capable of setting a second resolution that is greater than the first resolution. The photosensitive medium moving unit may move the photosensitive medium by a second velocity in the predetermined moving direction, the second velocity being smaller than the first velocity and allowing the value of the second interval to become equal to the first interval.
The multibeam scanning device may further comprise a light amount control unit that controls, when the resolution setting unit sets the first resolution, the light beam unit to set the light amounts of the first and second light beams to a first value, the light amount control unit controlling, when the resolution setting unit sets the second resolution, the light beam unit to set the light amounts of the first and second light beams to a second value, the first value being greater than the second value. A relationship between the first and second values of the light amounts corresponds to a relationship between the value of the second interval set for the first resolution and the value of the first interval.